We thank C. Park for reading the manuscript. This work was supported by the NIAMS under Award Number K01AR061434 and a Leukemia &#38; Lymphoma Society Fellowship Award (5127-09) to D.P and grants of the National Institutes of Health to C.P.L. and D.T.S. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

1. Mice and Preconditioning
Note: All mice were maintained in pathogen-free conditions and all protocols were approved by the Institutional Animal Care and Use Committee (IACUC) at the Massachusetts General Hospital. All surgery should be performed under sterile condition using autoclaved sterile equipment. Mx1-Cre15, Rosa26-loxP-stop-loxP-EYFP (Rosa-YFP), and Rosa26-loxP-stop-loxP-tdTomato (Rosa-Tomato), were purchased from Jackson Laboratories. Osteocalcin-GFP mice were provided by Dr. Henry Kronenberg. For the quantitative analysis of OSPC migration and proliferation in vivo, Mx1-Cre+Rosa-YFP+ (single color-reporter) mice were used. For more detailed tracking of their differentiation into Osteocalcin+ mature osteoblasts, we used trigenic Mx1-Cre+Rosa-Tomato+Ocn-GFP+ mice.
<ol>
	<li>To label Mx1+ cells in vivo, prepare polyinosinic-polycytidylic acid (pIpC, 2.5 mg/ml) in sterile PBS solution and inject 200 &#956;l for 20 g of Mx1-Cre+ reporter mouse intraperitoneally once every other day for 10 days.</li>
	<li>To eliminate resident Mx1+ hematopoietic cells, irradiate mice with a single dose of 9.5 Gy. After 24 hr of irradiation, transplant wild type bone marrow cells (1x106 cells/mouse) intravenously16. Note: Since Mx1-inducible cells include hematopoietic cells and hematopoietic-derived osteoclasts, the elimination of Mx1+ hematopoietic cells improves the imaging quality and quantitation of Mx1+ osteogenic cells.</li>
	<li>After bone marrow transplantation, monitor animals for four to six weeks in order to achieve a successful repopulation of donor marrow cells.</li>
</ol>
2. Mouse Preparation
<ol>
	<li>Anesthetize mouse by intraperitoneal injection of 50 &#956;l of ketamine/xylazine (100 mg/kg, xylazine 12 mg/kg body weight) using an IACUC-approved procedure. Note: Duration of the effect may be extended by an additional dose of ketamine/xylazine.</li>
	<li>Determine if the mouse is fully anesthetized by the lack of response to toe and/or tail pinches. (Optional) When the mouse is anesthetized, secure an isoflurane gas mask over the nose by taping. Adjust the level of isoflurane to ensure the animal is fully sedated.</li>
	<li>Clip the scalp hair using an electric trimmer or small scissors. Remove the hair fragments and sterilize the exposed skin with 70% alcohol swab. Apply tear gel to prevent corneal dehydration.</li>
</ol>
3. Microfracture Injury
<ol>
	<li>After ensuring the animal is fully sedated, make a single reverse L-shaped incision to open the scalp skin. Briefly, make a first transverse incision (less than 1 cm) starting from one ear to another ear. Turn ~60&#176; and continue to incise toward the nose until ~2-3 mm away from nose. Note: This incision minimizes the formation of scar tissues above the area to be imaged.</li>
	<li>Separate the skin flaps by pulling toward the sides with forceps. Both frontal bones and the intersection of sagittal and coronal sutures should be clearly exposed.</li>
	<li>Clean the open surface by flushing with sterile PBS and gentle wiping with sterile gauze or cotton swabs until all the residual hairs are eliminated.</li>
	<li>To generate microfractures on the calvarium, hold the mouse head with one hand and a 30 G needle with another hand. Make a micro-puncture (~0.2 mm diameter wound with &#60; 1 mm depth) on the left frontal bone near the intersection of the sagittal and coronal sutures by inserting the tip of a 30 G needle with gentle pressure and twisting motion. Caution: It is critical to avoid the needle from penetrating into the brain, thereby minimizing bleeding and tissue damage.</li>
	<li>Switch to a bigger needle (20 or 25 G) and widen the puncture hole by twisting the needle (~0.5 mm diameter).</li>
	<li>Repeat step 3.3-3.5 to generate second puncture on the contralateral frontal bone.</li>
	<li>Wipe out the injured spots by continuous dropping of PBS until the bleeding stops. 
	Note: Bleeding on fracture sites will interfere with appropriate imaging and induce scar formation.</li>
	<li>Apply a drop of sterile physiological saline solution or 2% Methocel on the skull to avoid drying. Note: Do not allow the skull surface to dry, which will reduce image clarity. It is important to use a sufficient amount of gel or saline to cover the area.</li>
</ol>
4. Intravital Imaging
<ol>
	<li>(Optional) Before imaging, some mice are injected with a vascular dye to visualize the blood vessels. Inject retro-orbitally with 20 &#956;l of non-targeted Qtracker 705 (2 &#956;M solution in 50 mM borate buffer) diluted in 80 ml of PBS. Use an insulin syringe to minimize reagent waste. If the signal is not sufficiently bright, additional amounts might be required.</li>
	<li>Turn on the scanner. Note: A polygon-based laser scanner allows simultaneous multi-channel image acquisition at video rate (30 frames per sec). Video rate scanning is very important for live animal imaging.</li>
	<li>Turn on the multi-photon laser (femto-second titanium:sapphire laser). Set the wavelength to 880 nm and adjust the power for second harmonic generation imaging (440 nm) of the bone. For GFP and tdTomato excitation, turn on the 491 nm and 561 nm solid-state lasers.</li>
	<li>Turn on the PMT (photomultiplier tube) detectors for each signal (a 435 &#177; 20 nm band-pass filter for second harmonic generation, a 528 &#177; 19 nm band-pass filter for GFP, and 590 &#177; 20 for tdTomato.) (Optional) Use a 638 nm helium&#8211;neon laser and a PMT with a 695 &#177; 27.5 nm band-pass filter to detect Qtracker 705 signal.</li>
	<li>Place the animal on a XYZ-axis motorized microscope stage. Keep the mouse in the most comfortable position with an electric heating pad to help maintain body temperature (this reduces the risk of animal loss). Use tape to hold the mouse to minimize movement during imaging and to keep the imaged area as horizontal as possible. </li>
	<li>Apply a drop of warm 2% methylcellulose gel or physiological saline solution on the skull to avoid drying. Put a cover glass on the imaging area. Use a low magnification lens (30x water-immersion objective with 0.9 NA) to scan the calvaria.</li>
	<li>Using the XYZ-axis controller, find the surface of calvaria by detecting the SHG signal from bones and identify a crucial landmark location, such as the intersection between the sagittal sutures and coronal sutures. Acquire an image and record the XYZ coordinates.</li>
	<li>Continue to search for the location of the injury by observing SHG and fluorescence signals.</li>
	<li>When injury sites or the region of interest are found, acquire an image of the best focal plane containing SHG and fluorescence signals from the cells of interest. Save XYZ coordinates and the distance to the intersection of the sagittal and coronal sutures to define their precise location for the next rounds of imaging.</li>
	<li>To collect 3D cellular and bone structures of fracture injury, record images by Z-stacks (2 - 5 &#956;m interval) with ~100 &#956;m depth from endosteal bone surface. After the completion of imaging of one side of injury, repeat imaging process for next injury sites.</li>
</ol>
5. Post Operation Procedures
<ol>
	<li>After imaging, rinse imaging site with sterile saline solution to remove the methylcellulose gel from the skull. Using a sterile cotton swab, apply a small amount of triple antibiotic ointment on the surface. Cover the skin flaps and re-close the scalp by surgical suturing. This can be done with a hypoallergenic suturing thread (absorbable polyglactin suture) and 5-0 size suture needle. Caution: Good suturing technique minimizes scar formation.</li>
	<li>Treat all animals with IP injection of 0.05-0.1 mg/kg buprenorphine every 12 hr for 48 hr following surgery. Keep animals in a warm recovery chamber until they regain sufficient consciousness. After 3 to 5 days, reopen the suture and repeat intravital imaging steps to track the cellular change during fracture healing.</li>
</ol>

<ol>
	<li>Harada, S., Rodan, G. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Control+of+osteoblast+function+and+regulation+of+bone+mass.">Control of osteoblast function and regulation of bone mass.</a> Nature. 423, 349-355 (2003).</li><li>Manolagas, S. C., Parfitt, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=What+old+means+to+bone.">What old means to bone.</a> Trends Endocrinol Metab. 21, 369-374 (2010).</li><li>Khosla, S., Riggs, B. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pathophysiology+of+age-related+bone+loss+and+osteoporosis.">Pathophysiology of age-related bone loss and osteoporosis.</a> Endocrinol Metab Clin North Am. 34, 1015-1030 (2005).</li><li>Friedenstein, A. J., Chailakhyan, R. K., Latsinik, N. V., Panasyuk, A. F., Keiliss-Borok, I. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stromal+cells+responsible+for+transferring+the+microenvironment+of+the+hemopoietic+tissues.+Cloning+in+vitro+and+retransplantation+in+vivo.">Stromal cells responsible for transferring the microenvironment of the hemopoietic tissues. Cloning in vitro and retransplantation in vivo.</a> Transplantation. 17, 331-340 (1974).</li><li>Mendez-Ferrer, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mesenchymal+and+haematopoietic+stem+cells+form+a+unique+bone+marrow+niche.">Mesenchymal and haematopoietic stem cells form a unique bone marrow niche.</a> Nature. 466, 829-834 (2010).</li><li>Park, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Endogenous+Bone+Marrow+MSCs+Are+Dynamic,+Fate-Restricted+Participants+in+Bone+Maintenance+and+Regeneration.">Endogenous Bone Marrow MSCs Are Dynamic, Fate-Restricted Participants in Bone Maintenance and Regeneration.</a> Cell Stem Cell. 10, 259-272 (2012).</li><li>Schindeler, A., McDonald, M. M., Bokko, P., Little, D. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bone+remodeling+during+fracture+repair:+The+cellular+picture.">Bone remodeling during fracture repair: The cellular picture.</a> Semin Cell Dev Biol. 19, 459-466 (2008).</li><li>Holstein, J. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapamycin+affects+early+fracture+healing+in+mice.">Rapamycin affects early fracture healing in mice.</a> Br J Pharmacol. 154, 1055-1062 (2008).</li><li>Maes, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Osteoblast+precursors,+but+not+mature+osteoblasts,+move+into+developing+and+fractured+bones+along+with+invading+blood+vessels.">Osteoblast precursors, but not mature osteoblasts, move into developing and fractured bones along with invading blood vessels.</a> Dev Cell. 19, 329-344 (2010).</li><li>Grcevic, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vivo+fate+mapping+identifies+mesenchymal+progenitor+cells.">In vivo fate mapping identifies mesenchymal progenitor cells.</a> Stem Cells. 30, 187-196 (2012).</li><li>O'Neill, K. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Micro-computed+tomography+assessment+of+the+progression+of+fracture+healing+in+mice.">Micro-computed tomography assessment of the progression of fracture healing in mice.</a> Bone. 50, 1357-1367 (2012).</li><li>Kovar, J. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Near-infrared-labeled+tetracycline+derivative+is+an+effective+marker+of+bone+deposition+in+mice.">Near-infrared-labeled tetracycline derivative is an effective marker of bone deposition in mice.</a> Anal Biochem. 416, 167-173 (2011).</li><li>Mayer-Kuckuk, P., Boskey, A. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+imaging+promotes+progress+in+orthopedic+research.">Molecular imaging promotes progress in orthopedic research.</a> Bone. 39, 965-977 (2006).</li><li>Lo Celso, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Live-animal+tracking+of+individual+haematopoietic+stem/progenitor+cells+in+their+niche.">Live-animal tracking of individual haematopoietic stem/progenitor cells in their niche.</a> Nature. 457, 92-96 (2009).</li><li>Kuhn, R., Schwenk, F., Aguet, M., Rajewsky, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inducible+gene+targeting+in+mice.">Inducible gene targeting in mice.</a> Science. 269, 1427-1429 (1995).</li><li>Duran-Struuck, R., Dysko, R. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Principles+of+bone+marrow+transplantation+(BMT):+providing+optimal+veterinary+and+husbandry+care+to+irradiated+mice+in+BMT+studies.">Principles of bone marrow transplantation (BMT): providing optimal veterinary and husbandry care to irradiated mice in BMT studies.</a> Journal of the American Association for Laboratory Animal Science: JAALAS. 48, 11-22 (2009).</li><li>Tu, Q., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Osterix+overexpression+in+mesenchymal+stem+cells+stimulates+healing+of+critical-sized+defects+in+murine+calvarial+bone.">Osterix overexpression in mesenchymal stem cells stimulates healing of critical-sized defects in murine calvarial bone.</a> Tissue Eng. 13, 2431-2440 (2007).</li></ol>

The authors declare that they have no competing financial Interests.

The regulation of skeletal stem cells may be of great importance for defining better methods to achieve bone regeneration. Quantitative and sequential imaging at the cellular level has been technically challenging. Although the mouse long-bone fracture model has been widely used and suitable for biomechanical studies 17, its deep tissue location, uneven fracture size, soft tissue damage, and the application of stabilizing fixators have limited sequential intravital imaging. Here, a method to overcome these lim...

Degenerative bone diseases and age-related bone loss leading to a high risk of osteoporotic fracture has become a major challenge in public health1. Bone maintenance is controlled by bone-forming osteoblasts and bone-resorbing osteoclasts. Defects of bone forming cells are a main cause of age-related bone loss and degenerative bone diseases2,3. While extensive research has focused on the improvement of fracture healing, the discovery of reliable drugs to cure degenerative bone diseases and to reverse the weakness of osteoporotic fractures remains an important issue. Thus, studying the source of bone forming cells and their control mechanisms in bone regeneration and repair provides a novel insight to enhance skeletal regeneration and reverse bone loss diseases.
The existence of multipotent mesenchymal cells in bone marrow has been proposed based on the identification of clonogenic populations that could differentiate into osteogenic, adipogenic and chondrogenic lineages ex vivo4. Recently, multiple studies have reported that skeletal/mesenchymal stem cells (SSCs/MSCs) are a natural source of osteoblasts and are critical for bone turnover, remodeling, and fracture repair5,6. In addition, our lineage-tracing study revealed that mature osteoblasts have a unexpectedly short half-life (~60 days) and are continuously replenished by their stem/progenitor cells in both normal homeostatic and fracture repair conditions6. However, the in vivo identity of stem cells and how such cells react to fracture injury and supply bone-forming cells are unclear. Therefore, it is important to develop a method that is able to analyze the migration, proliferation and differentiation of endogenous SSCs/MSCs in under physiological circumstances.
Fracture repair is a multi-cellular and dynamic process regulated by an array of complex cytokines and growth factors7. The most popular approach for fracture studies is to use an animal model with long-bone fracture and to analyze bones by bone sectioning and immunofluorescent techniques8-10. This repair process can be monitored by multiple imaging techniques including micro-CT11, near-infrared fluorescence12, and chemiluminescence imaging13. However, each technique has certain limitations and there has been no effective way to monitor SSCs/MSC function at the cellular level in vivo. Recently, confocal/two-photon intravital microscopy has been developed and used to detect transplanted cancer cells and hematopoietic stem cells in the context of their bone marrow microenvironment even at single-cell resolution in living animals14. By combining this technology with a series of lineage tracing models, we were able to define that osteogenic stem/progenitor cells can be genetically marked by transient activation of the myxovirus resistance-1 (Mx1) promoter and Mx1-induced progenitors can maintain the majority of mature osteoblasts over time but do not participate in the generation of chondrocytes in the adult mouse6. In addition, we demonstrated that Mx1-labeled OSPCs supply the majority of new osteoblasts in fracture healing6.
Here, using osteo-lineage tracking models and intravital microscopy, a protocol is provided to define the in vivo kinetics of Mx1+&#160;osteogenic stem/progenitor cells in fracture repair. This protocol offers sequential imaging to track the relocation of osteogenic stem/progenitors into fracture sites and the quantitative measurement of osteoprogenitor expansion in the early repair process. This approach may be useful in multiple contexts including the evaluation of therapeutic candidates to improve bone repair.

<table border="0" cellpadding="0" cellspacing="0" width="829">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">C57BL/6J (H-2b)</td>
			<td style="width:140px;">Jackson Laboratories (Bar Harbor, ME)</td>
			<td style="width:195px;">000664</td>
			<td style="width:279px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Ketamine Hydrochloride Injection</td>
			<td style="width:140px;">Bionichepharma</td>
			<td style="width:195px;">67457-001-10</td>
			<td>&#160;Vial size: 10 ml (50 mg/ml)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Xylazine Sterile Solution</td>
			<td style="width:140px;">Lloyd Inc.</td>
			<td style="width:195px;">NADA# 139-236</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Buprenorphine Hl</td>
			<td style="width:140px;">BEDFORD LAB</td>
			<td style="width:195px;">NDC 55390-100-10</td>
			<td>Vial: 0.3 mg/ml, Doses: 0.05-0.1 mg/kg</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">DPBS, 1X</td>
			<td style="width:140px;">CORNING cellgro</td>
			<td style="width:195px;">21-031-CV</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Alcohol Prep Pads (70% Isopropyl alcohol)</td>
			<td style="width:140px;">Kendall WEBCOL</td>
			<td style="width:195px;">5110</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Fine Surgical Scissor</td>
			<td style="width:140px;">F.S.T</td>
			<td style="width:195px;">14568-09</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Extra fine Forceps</td>
			<td style="width:140px;">F.S.T</td>
			<td style="width:195px;">11150-10</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">VICRYL*Plus Suture</td>
			<td style="width:140px;">Ethicon</td>
			<td style="width:195px;">VCP490G</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Qtracker 705 non-targeted quantum dot</td>
			<td style="width:140px;">Invitrogen</td>
			<td style="width:195px;">Q21061</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Methocel 2%</td>
			<td style="width:140px;">OmmiVision</td>
			<td style="width:195px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">pIpC (Polyinosinic-polycytidylic acid)&#160;&#160;</td>
			<td style="width:140px;">Sigma</td>
			<td style="width:195px;">P0913-50MG</td>
			<td>100 &#956;l (2.5 mg/ml in PBS) for 10 g of mouse</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Mai Tai Tunable Ultrafast Lasers</td>
			<td style="width:140px;">Spectra Physics</td>
			<td style="width:195px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Dual Calypso 491 + 532 nm DPSS laser</td>
			<td style="width:140px;">Cobolt AB</td>
			<td style="width:195px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Radius-635 HeNe laser</td>
			<td style="width:140px;">Coherent</td>
			<td style="width:195px;"></td>
			<td></td>
		</tr>
	</tbody>
</table>

sequential in vivo imaging of osteogenic stem/progenitor cells during fracture repair

Bone turns over continuously and is highly regenerative following injury. Osteogenic stem/progenitor cells have long been hypothesized to exist, but in vivo demonstration of such cells has only recently been attained. Here, in vivo imaging techniques to investigate the role of endogenous osteogenic stem/progenitor cells (OSPCs) and their progeny in bone repair are provided. Using osteo-lineage cell tracing models and intravital imaging of induced microfractures in calvarial bone, OSPCs can be directly observed during the first few days after injury, in which critical events in the early repair process occur. Injury sites can be sequentially imaged revealing that OSPCs relocate to the injury, increase in number and differentiate into bone forming osteoblasts. These methods offer a means of investigating the role of stem cell-intrinsic and extrinsic molecular regulators for bone regeneration and repair.

The stabilized long bone fracture model has been popular in fracture studies. However, long bone or large fracture models cause multiple tissue damage and therefore, have a limitation in quantitative measurement of bone cell function. We developed a minimally invasive injury (less than 1 mm diameter with minimal or no invasion into the dura mater) on calvarial frontal bones with needle drilling (Figures 1A-1C). We chose a top view of the calvarial frontal bones for in vivo live imaging of microf...

Watch this Scientific Journal Video about Sequential In vivo Imaging of Osteogenic Stem/Progenitor Cells During Fracture Repair at JoVE.com

Sequential In vivo Imaging of Osteogenic Stem/Progenitor Cells During Fracture Repair

Quantitative measurement of bone progenitor function in fracture healing requires high resolution serial imaging technology. Here, protocols are provided for using intravital microscopy and osteo-lineage tracking to sequentially image and quantify the migration, proliferation and differentiation of endogenous osteogenic stem/progenitor cells in the process of repairing bone fracture.

Sequential In vivo Imaging of Osteogenic Stem/Progenitor Cells During Fracture Repair

Bone turns over continuously and is highly regenerative following injury. Osteogenic stem/progenitor cells have long been hypothesized to exist, but in ...

sequential-vivo-imaging-osteogenic-stemprogenitor-cells-during

Research

JoVE Journal

Medicine

10.5K vues.  Harvard Stem Cell Institute.  La mesure quantitative de la fonction progénitrices de l'os dans la guérison des fractures nécessite haute résolution technologie d'imagerie de série. Ici, les protocoles sont fournies à l'aide de la microscopie intravitale suivi et l'ostéo-lignée pour quantifier séquentiellement l'image et la migration, la prolifération et la différenciation des cellules souches / progénitrices ostéogéniques endogènes dans le processus de réparation d...

Vidéo: Sequential In vivo Imaging of Osteogenic Stem/Progenitor Cells During Fracture Repair

In vivo Dual Substrate Bioluminescent Imaging

Our understanding of how and when breast cancer cells transit from established primary tumors to metastatic sites has increased at an exceptional rate since the advent of in vivo bioluminescent imaging technologies 1-3. Indeed, the ability to locate and quantify tumor growth longitudinally in a single cohort of animals to completion of the study as opposed to sacrificing individual groups of animals at specific assay times has revolutionized how researchers investigate breast cancer metastasis. Unfortunately, current methodologies preclude the real-time assessment of critical changes that transpire in cell signaling systems as breast cancer cells (i) evolve within primary tumors, (ii) disseminate throughout the body, and (iii) reinitiate proliferative programs at sites of a metastatic lesion. However, recent advancements in bioluminescent imaging now make it possible to simultaneously quantify specific spatiotemporal changes in gene expression as a function of tumor development and metastatic progression via the use of dual substrate luminescence reactions. To do so, researchers take advantage for two light-producing luciferase enzymes isolated from the firefly (Photinus pyralis) and sea pansy (Renilla reniformis), both of which react to mutually exclusive substrates that previously facilitated their wide-spread use in in vitro cell-based reporter gene assays 4. Here we demonstrate the in vivo utility of these two enzymes such that one luminescence reaction specifically marks the size and location of a developing tumor, while the second luminescent reaction serves as a means to visualize the activation status of specific signaling systems during distinct stages of tumor and metastasis development. Thus, the objectives of this study are two-fold. First, we will describe the steps necessary to construct dual bioluminescent reporter cell lines, as well as those needed to facilitate their use in visualizing the spatiotemporal regulation of gene expression during specific steps of the metastatic cascade. Using the 4T1 model of breast cancer metastasis, we show that the in vivo activity of a synthetic Smad Binding Element (SBE) promoter was decreased dramatically in pulmonary metastasis as compared to that measured in the primary tumor 4-6. Recently, breast cancer metastasis was shown to be regulated by changes within the primary tumor microenvironment and reactive stroma, including those occurring in fibroblasts and infiltrating immune cells 7-9. Thus, our second objective will be to demonstrate the utility of dual bioluminescent techniques in monitoring the growth and localization of two unique cell populations harbored within a single animal during breast cancer growth and metastasis.

In vivo Dual Substrate Bioluminescent Imaging

Herein we describe the methods to construct, visualize, and quantify the bioluminescent reactions of both firefly and renilla luciferase enzymes expressed in metastatic breast cancer cells during their growth and metastasis in vivo.

Our understanding of how and when breast cancer cells transit from established primary tumors to metastatic sites has increased at an exceptional rate ...

3D-Neuronavigation In Vivo Through a Patient's Brain During a Spontaneous Migraine Headache

A growing body of research, generated primarily from MRI-based studies, shows that migraine appears to occur, and possibly endure, due to the alteration of specific neural processes in the central nervous system. However, information is lacking on the molecular impact of these changes, especially on the endogenous opioid system during migraine headaches, and neuronavigation through these changes has never been done. This study aimed to investigate, using a novel 3D immersive and interactive neuronavigation (3D-IIN) approach, the endogenous &#181;-opioid transmission in the brain during a migraine headache attack in vivo. This is arguably one of the most central neuromechanisms associated with pain regulation, affecting multiple elements of the pain experience and analgesia. A 36 year-old female, who has been suffering with migraine for 10 years, was scanned in the typical headache (ictal) and nonheadache (interictal) migraine phases using Positron Emission Tomography (PET) with the selective radiotracer [11C]carfentanil, which allowed us to measure &#181;-opioid receptor availability in the brain (non-displaceable binding potential - &#181;OR BPND). The short-life radiotracer was produced by a cyclotron and chemical synthesis apparatus on campus located in close proximity to the imaging facility. Both PET scans, interictal and ictal, were scheduled during separate mid-late follicular phases of the patient's menstrual cycle. During the ictal PET session her spontaneous headache attack reached severe intensity levels; progressing to nausea and vomiting at the end of the scan session. There were reductions in &#181;OR BPND in the pain-modulatory regions of the endogenous &#181;-opioid system during the ictal phase, including the cingulate cortex, nucleus accumbens (NAcc), thalamus (Thal), and periaqueductal gray matter (PAG); indicating that &#181;ORs were already occupied by endogenous opioids released in response to the ongoing pain. To our knowledge, this is the first time that changes in &#181;OR BPND during a migraine headache attack have been neuronavigated using a novel 3D approach. This method allows for interactive research and educational exploration of a migraine attack in an actual patient's neuroimaging dataset.

3D-Neuronavigation In Vivo Through a Patient&#039;s Brain During a Spontaneous Migraine Headache

In this study, the authors report for the first time a novel 3D-Immersive &#38; Interactive Neuronavigation (3D-IIN) through the impact of a spontaneous migraine headache attack in the &#956;-opioid system of a patient's brain in vivo.

A growing body of research, generated primarily from MRI-based studies, shows that migraine appears to occur, and possibly endure, due to the alteration ...

In vivo 19F MRI for Cell Tracking

In vivo 19F MRI allows quantitative cell tracking without the use of ionizing radiation. It is a noninvasive technique that can be applied to humans. Here, we describe a general protocol for cell labeling, imaging, and image processing. The technique is applicable to various cell types and animal models, although here we focus on a typical mouse model for tracking murine immune cells. The most important issues for cell labeling are described, as these are relevant to all models. Similarly, key imaging parameters are listed, although the details will vary depending on the MRI system and the individual setup. Finally, we include an image processing protocol for quantification. Variations for this, and other parts of the protocol, are assessed in the Discussion section. Based on the detailed procedure described here, the user will need to adapt the protocol for each specific cell type, cell label, animal model, and imaging setup. Note that the protocol can also be adapted for human use, as long as clinical restrictions are met.

In vivo 19F MRI for Cell Tracking

We describe a general protocol for in vivo cell tracking using MRI in a mouse model with ex vivo labeled cells. A typical protocol for cell labeling, image acquisition processing and quantification is included.

In vivo 19F MRI allows quantitative cell tracking without the use of ionizing radiation. It is a noninvasive technique that can be applied to humans. ...

In Vivo Dynamics of Retinal Microglial Activation During Neurodegeneration: Confocal Ophthalmoscopic Imaging and Cell Morphometry in Mouse Glaucoma

Microglia, which are CNS-resident neuroimmune cells, transform their morphology and size in response to CNS damage, switching to an activated state with distinct functions and gene expression profiles. The roles of microglial activation in health, injury and disease remain incompletely understood due to their dynamic and complex regulation in response to changes in their microenvironment. Thus, it is critical to non-invasively monitor and analyze changes in microglial activation over time in the intact organism. In vivo studies of microglial activation have been delayed by technical limitations to tracking microglial behavior without altering the CNS environment. This has been particularly challenging during chronic neurodegeneration, where long-term changes must be tracked. The retina, a CNS organ amenable to non-invasive live imaging, offers a powerful system to visualize and characterize the dynamics of microglia activation during chronic disorders.
This protocol outlines methods for long-term, in vivo imaging of retinal microglia, using confocal ophthalmoscopy (cSLO) and CX3CR1GFP/+ reporter mice, to visualize microglia with cellular resolution. Also, we describe methods to quantify monthly changes in cell activation and density in large cell subsets (200-300 cells per retina). We confirm the use of somal area as a useful metric for live tracking of microglial activation in the retina by applying automated threshold-based morphometric analysis of in vivo images. We use these live image acquisition and analyses strategies to monitor the dynamic changes in microglial activation and microgliosis during early stages of retinal neurodegeneration in a mouse model of chronic glaucoma. This approach should be useful to investigate the contributions of microglia to neuronal and axonal decline in chronic CNS disorders that affect the retina and optic nerve.

In Vivo Dynamics of Retinal Microglial Activation During Neurodegeneration: Confocal Ophthalmoscopic Imaging and Cell Morphometry in Mouse Glaucoma

Microglia activation and microgliosis are key responses to chronic neurodegeneration. Here, we present methods for in vivo, long-term visualization of retinal CX3CR1-GFP+ microglial cells by confocal ophthalmoscopy, and for threshold and morphometric analyses to identify and quantify their activation. We monitor microglial changes during early stages of age-related glaucoma.

Microglia, which are CNS-resident neuroimmune cells, transform their morphology and size in response to CNS damage, switching to an activated state with ...

In Vivo Imaging and Tracking of Technetium-99m Labeled Bone Marrow Mesenchymal Stem Cells in Equine Tendinopathy

Recent advances in the application of bone marrow mesenchymal stem cells (BMMSC) for the treatment of tendon and ligament injuries in the horse suggest improved outcome measures in both experimental and clinical studies. Although the BMMSC are implanted into the tendon lesion in large numbers (usually 10 - 20 million cells), only a relatively small number survive (&#60;10%) although these can persist for up to 5 months after implantation. This appears to be a common observation in other species where BMMSC have been implanted into other tissues and it is important to understand when this loss occurs, how many survive the initial implantation process and whether the cells are cleared into other organs. Tracking the fate of the cells can be achieved by radiolabeling the BMMSC prior to implantation which allows non-invasive in vivo imaging of cell location and quantification of cell numbers.
This protocol describes a cell labeling procedure that uses Technetium-99m (Tc-99m), and tracking of these cells following implantation into injured flexor tendons in horses. Tc-99m is a short-lived (t1/2 of 6.01 hr) isotope that emits gamma rays and can be internalized by cells in the presence of the lipophilic compound hexamethylpropyleneamine oxime (HMPAO). These properties make it ideal for use in nuclear medicine clinics for the diagnosis of many different diseases. The fate of the labeled cells can be followed in the short term (up to 36 hr) by gamma scintigraphy to quantify both the number of cells retained in the lesion and distribution of the cells into lungs, thyroid and other organs. This technique is adapted from the labeling of blood leukocytes and could be utilized to image implanted BMMSC in other organs.

In Vivo Imaging and Tracking of Technetium-99m Labeled Bone Marrow Mesenchymal Stem Cells in Equine Tendinopathy

This protocol describes the radiolabeling of equine mesenchymal stem cells and their implantation into tendon injuries in the horse in order to determine cell survival and tissue distribution using gamma scintigraphy.

Recent advances in the application of bone marrow mesenchymal stem cells (BMMSC) for the treatment of tendon and ligament injuries in the horse suggest ...

Studying Pancreatic Cancer Stem Cell Characteristics for Developing New Treatment Strategies

Pancreatic ductal adenocarcinoma (PDAC) contains a subset of exclusively tumorigenic cancer stem cells (CSCs) which have been shown to drive tumor initiation, metastasis and resistance to radio- and chemotherapy. Here we describe a specific methodology for culturing primary human pancreatic CSCs as tumor spheres in anchorage-independent conditions. Cells are grown in serum-free, non-adherent conditions in order to enrich for CSCs while their more differentiated progenies do not survive and proliferate during the initial phase following seeding of single cells. This assay can be used to estimate the percentage of CSCs present in a population of tumor cells. Both size (which can range from 35 to 250 micrometers) and number of tumor spheres formed represents CSC activity harbored in either bulk populations of cultured cancer cells or freshly harvested and digested tumors 1,2. Using this assay, we recently found that metformin selectively ablates pancreatic CSCs; a finding that was subsequently further corroborated by demonstrating diminished expression of pluripotency-associated genes/surface markers and reduced in vivo tumorigenicity of metformin-treated cells. As the final step for preclinical development we treated mice bearing established tumors with metformin and found significantly prolonged survival. Clinical studies testing the use of metformin in patients with PDAC are currently underway (e.g., NCT01210911, NCT01167738, and NCT01488552). Mechanistically, we found that metformin induces a fatal energy crisis in CSCs by enhancing reactive oxygen species (ROS) production and reducing mitochondrial transmembrane potential. In contrast, non-CSCs were not eliminated by metformin treatment, but rather underwent reversible cell cycle arrest. Therefore, our study serves as a successful example for the potential of in vitro sphere formation as a screening tool to identify compounds that potentially target CSCs, but this technique will require further in vitro and in vivo validation to eliminate false discoveries.

Pancreatic cancer stem cells (CSCs) can be expanded in vitro using the anchorage-independent sphere culture technique, which represents a powerful tool to study CSC biology and can serve as the first step to develop novel CSC-targeting therapies. Here the methodology for expanding, analyzing and targeting of pancreatic CSCs is provided.

Pancreatic ductal adenocarcinoma (PDAC) contains a subset of exclusively tumorigenic cancer stem cells (CSCs) which have been shown to drive tumor ...

Depletion of Mouse Cells from Human Tumor Xenografts Significantly Improves Downstream Analysis of Target Cells

The use of in vitro cell line models for cancer research has been a useful tool. However, it has been shown that these models fail to reliably mimic patient tumors in different assays1. Human tumor xenografts represent the gold standard with respect to tumor biology, drug discovery, and metastasis research 2-4. Tumor xenografts can be derived from different types of material like tumor cell lines, tumor tissue from primary patient tumors4 or serially transplanted tumors. When propagated in vivo, xenografted tissue is infiltrated and vascularized by cells of mouse origin. Multiple factors such as the tumor entity, the origin of xenografted material, growth rate and region of transplantation influence the composition and the amount of mouse cells present in tumor xenografts. However, even when these factors are kept constant, the degree of mouse cell contamination is highly variable.
Contaminating mouse cells significantly impair downstream analyses of human tumor xenografts. As mouse fibroblasts show high plating efficacies and proliferation rates, they tend to overgrow cultures of human tumor cells, especially slowly proliferating subpopulations. Mouse cell derived DNA, mRNA, and protein components can bias downstream gene expression analysis, next-generation sequencing, as well as proteome analysis 5. To overcome these limitations, we have developed a fast and easy method to isolate untouched human tumor cells from xenografted tumor tissue. This procedure is based on the comprehensive depletion of cells of mouse origin by combining automated tissue dissociation with the benchtop tissue dissociator and magnetic cell sorting. Here, we demonstrate that human target cells can be can be obtained with purities higher than 96% within less than 20 min independent of the tumor type.

Human tumor xenografts are vascularized and infiltrated by cells of mouse origin during the growth phase in vivo. To circumvent the bias caused by these contaminating cells during downstream analysis, we developed a method allowing for comprehensive depletion of all mouse cells by magnetic cell sorting.

The use of in vitro cell line models for cancer research has been a useful tool. However, it has been shown that these models fail to reliably mimic ...

In Vivo Evaluation of Fracture Callus Development During Bone Healing in Mice Using an MRI-compatible Osteosynthesis Device for the Mouse Femur

Endochondral fracture healing is a complex process involving the development of fibrous, cartilaginous, and osseous tissue in the fracture callus. The amount of the different tissues in the callus provides important information on the fracture healing progress. Available in vivo techniques to longitudinally monitor the callus tissue development in preclinical fracture-healing studies using small animals include digital radiography and &#181;CT imaging. However, both techniques are only able to distinguish between mineralized and non-mineralized tissue. Consequently, it is impossible to discriminate cartilage from fibrous tissue. In contrast, magnetic resonance imaging (MRI) visualizes anatomical structures based on their water content and might therefore be able to noninvasively identify soft tissue and cartilage in the fracture callus. Here, we report the use of an MRI-compatible external fixator for the mouse femur to allow MRI scans during bone regeneration in mice. The experiments demonstrated that the fixator and a custom-made mounting device allow repetitive MRI scans, thus enabling longitudinal analysis of fracture-callus tissue development.

In Vivo Evaluation of Fracture Callus Development During Bone Healing in Mice Using an MRI-compatible Osteosynthesis Device for the Mouse Femur

The evaluation of tissue development in the fracture callus during endochondral bone healing is essential to monitor the healing process. Here, we report the use of a magnetic resonance imaging (MRI)-compatible external fixator for the mouse femur to allow MRI scans during bone regeneration in mice.

Endochondral fracture healing is a complex process involving the development of fibrous, cartilaginous, and osseous tissue in the fracture callus. The ...

Middle Cerebral Artery Occlusion Allowing Reperfusion via Common Carotid Artery Repair in Mice

The ischemic stroke is a major cause of adult long-term disability and death worldwide. The current treatments available are limited, with only tissue plasminogen activator (tPA) as an approved drug treatment to target ischemic strokes. Current research in the field of ischemic stroke focuses on better understanding the pathophysiology of stroke, to develop and investigate novel pharmaceutical targets. Reliable experimental stroke models are crucial for the progression of potential treatments. The middle cerebral artery occlusion (MCAO) model is clinically relevant and the most frequently used surgical model of ischemic stroke in rodents. However, the outcomes of this model, such as lesion volume, are associated with high levels of variability, particularly in mice. The alternative MCAO model described here allows the reperfusion of the common carotid artery (CCA) and the increased perfusion of the middle cerebral artery (MCA) territory, using a tissue pad with fibrinogen-based sealant to repair the vessel, and the improved welfare of the mice by avoiding external carotid artery (ECA) ligation. This reduces the reliance on the Circle of Willis, which is known to be highly anatomically variable in mice. Representative data show that using this alternative surgical approach decreases the variability in lesion volumes between the traditional MCAO approach and the alternative approach described here.

Intraluminal filament occlusion of the middle cerebral artery is the most frequently used in vivo model of experimental stroke in rodents. An alternative surgical approach to allow common carotid artery repair is performed here, which allows the reperfusion of the common carotid artery and a full reperfusion to the middle cerebral artery territory.

The ischemic stroke is a major cause of adult long-term disability and death worldwide. The current treatments available are limited, with only tissue ...

A Simplified Stepwise Approach to Echo Guidance during Percutaneous Mitral Valve Repair

Percutaneous transcatheter edge-to-edge reconstruction of the mitral valve is a safe and well-established therapy for severe symptomatic mitral regurgitation in patients with high surgical risk. Echocardiographic guidance in addition to fluoroscopy is the gold standard and should be performed using a standardized technique.
This article lays out our reproducible step by step echocardiographic guide including views, measurements as well as highlighting possible difficulties that may arise during the procedure.
This article provides detailed and chronological echocardiographic views for each step of the procedure, especially preferences between 2D and 3D imaging. If needed, pulse wave, continuous wave and color doppler measurements are described. Furthermore, as there are no official recommendations for the quantification of mitral regurgitation during the percutaneous edge-to-edge-repair procedure, advice is also included for echocardiographic quantification after grasping the mitral leaflets and after device deployment. In addition, the article deals with important echocardiographic views to prevent and deal with possible complications during the procedure.
Echocardiographic guidance during transcatheter mitral valve repair is mandatory. A structured approach improves the collaboration between interventionist and imager and is indispensable for a safe and effective procedure.

This protocol presents in detail how to perform real-time echocardiographic guidance during transcatheter mitral valve repair. The fundamental views and the necessary measurements are described for each stage of the procedure.